This invention relates to a lithium ion battery construction for producing a high energy density output.
Various applications, such as in hybrid electric vehicles (HEV), require batteries exhibiting a high energy density output. xe2x80x9cEnergy densityxe2x80x9d refers to the ratio of the energy available from a battery to the weight or volume of the battery.
The present invention is directed to a lithium ion battery, and fabrication method therefor, configured to yield a high energy density output by minimizing head space, i.e., wasted interior volume, within the battery case and/or by reducing electrical energy losses internal to the battery.
A battery in accordance with the present invention includes a metal case comprised of a thin peripheral wall, e.g., cylindrical, surrounding an interior volume. In accordance with a preferred embodiment, the interior volume is substantially fully occupied by an electrode assembly comprised of a positive electrode strip, a negative electrode strip, and separator strips, superimposed on one another and helically wound to form a so called xe2x80x9cjelly rollxe2x80x9d. The positive electrode strip is formed of a metal substrate or foil, e.g., aluminum, having positive active material formed on both faces thereof. The negative electrode strip is formed of a metal substrate or foil, e.g., copper, having negative active material formed on both faces thereof.
In accordance with the invention, a set of multiple negative tabs extend from spaced locations along the negative electrode substrate toward the upper end of the case peripheral wall. A set of multiple positive spaced tabs extend from the positive electrode substrate toward the lower end of the case peripheral wall.
In accordance with a preferred embodiment of the invention, the negative tabs are electrically connected to a current collector, i.e., a metal ring, mounted within the interior volume adjacent to the upper end of the case peripheral wall. The metal ring is insulated from the peripheral wall, preferably by a concentric dielectric ring.
In further accordance with the preferred embodiment, the positive tabs are electrically connected to the peripheral wall by first folding them over the lower wall edge. A conductive end cap is mounted against the peripheral wall lower edge to pinch and electrically connect the positive tabs therebetween. The end cap is then sealed to the case peripheral wall, e.g., by laser welding, to completely seal the battery lower end and electrically connect the positive tabs to the case peripheral wall.